Nonwoven structures have long been known and used, for example, in papermaking and felting operations. More recently, alternative techniques have been used to form coherent webs of fibrous materials. For example, nonwoven structures can be made using cotton processing technology, including the use of cards and garnets. Carded webs tend to be light weight. To make thicker webs, multiple cards, transverse folding of the web or "crosslapping" can be used. Garnets can also be used to make a thick web from one or more fibers and/or fabric waste.
Airlaid webs represent still another approach to making nonwoven products. There, a heavy pulp sheet is defibered in a hammermill or pin mill into individual pulp fibers in an air stream. The air borne dispersed fibers are condensed, via vacuum, onto a porous belt, forming a planar web. The fibers are deposited, in a horizontal orientation, on the porous belt. Multiple layers can be built up, but there is little strength between layers.
The various products made using these techniques, because of their limited strength, are often further treated by a variety of bonding techniques. Mechanical bonding techniques have included needle punching, stitch bonding, and hydroentangling. Chemical bonding techniques generally involve a latex application. In thermal bonding techniques, a fusible substance, generally a powder or fiber, is used to form a support of unbonded fibers into a connected network.
While certain of the mechanical processing techniques described above, such as needle felting, stitchbonding and hydroentangling, can provide some strength in the thickness direction, they do not function on an individual fiber basis, and crosslapped structures, or even those which have been treated with latex bonding or using binder fiber, still have little strength in the thickness direction, that is, the direction normal or perpendicular to the major plane of the web. Such products accordingly have limited utility in multiple use applications.